Organic light-emitting devices are devices that utilize light emitted when excitons of fluorescent organic compounds return to the ground state, the excitons being generated by sandwiching between an anode and a cathode a thin film that contains a fluorescent compound and injecting electrons and holes (positive holes) from the respective electrodes.
A study by Eastman Kodak Company in 1987 (Non-patent reference 1) has reported that a light emission of about 1000 cd/m2 was observed under an applied voltage of about 10 V. In the study, the device had a separated-function type bilayer structure and used ITO as the anode, magnesium-silver alloy as the cathode, an aluminum quinolinol complex as an electron-carrying material and light-emitting material, and a triphenylamine derivative as a hole-carrying material. Related patent documents include the patent references 1 to 3.
Moreover, various light emissions from ultraviolet to infrared can be accomplished by using various different fluorescent organic compounds. Recently, active studies have been conducted on various compounds. Such studies are disclosed, for example, in the Patent references 4 to 11.
In addition to the organic light-emitting devices using small molecular materials as described above, organic light-emitting devices using conjugated polymers have been reported by a group of Cambridge University (non-patent reference 2). This report has disclosed that a film of polyphenylenevinylene (PPV) was formed by a coating method and it was confirmed that a single layer of the film emitted light. Related patent documents on organic light-emitting devices using conjugated polymers include the patent references 12 to 16.
As described above, a remarkable progress has been made in the field of organic light-emitting devices. The characteristic feature of such progress is that it enables production of light-emitting devices that exhibit high brightness even with a low application voltage, diversity in terms of emission wavelengths, and rapid response, with a thin and lightweight construction, which suggests a wide range of possible applications of the devices.
There are, however, still many problems with regard to durability, such as change with time due to prolonged use and deterioration due to moisture and the atmospheric gas containing oxygen. Moreover, for applications to a full-color display etc., light emissions exhibiting higher brightness or higher conversion efficiency, as well as blue, green, and red light emissions with higher color purities, are necessary with the current state of the art. For example, the patent reference 17 discloses diamine compounds as high emission efficiency materials, but blue-light emission showing high color purity (chromaticity coordinates: (x, y)=(0.14-0.15, 0.09-0.12)) has not been obtained yet.    (Patent Reference 1)    U.S. Pat. No. 4,539,507    (Patent Reference 2)    U.S. Pat. No. 4,720,432    (Patent Reference 3)    U.S. Pat. No. 4,885,211    (Patent Reference 4)    U.S. Pat. No. 5,151,629    (Patent Reference 5)    U.S. Pat. No. 5,409,783    (Patent Reference 6)    U.S. Pat. No. 5,382,477    (Patent Reference 7)    Japanese Patent Application Laid-Open No. 2-247278    (Patent Reference 8)    Japanese Patent Application Laid-Open No. 3-255190    (Patent Reference 9)    Japanese Patent Application Laid-Open No. 5-202356    (Patent Reference 10)    Japanese Patent Application Laid-Open No. 9-202878    (Patent Reference 11)    Japanese Patent Application Laid-Open No. 9-227576    (Patent Reference 12)    U.S. Pat. No. 5,247,190    (Patent Reference 13)    U.S. Pat. No. 5,514,878    (Patent Reference 14)    U.S. Pat. No. 5,672,678    (Patent Reference 15)    Japanese Patent Application Laid-Open No. 4-145192    (Patent Reference 16)    Japanese Patent Application Laid-Open No. 5-247460    (Patent Reference 17)    Japanese Patent Application Laid-Open No. 2001-52868    (Non-Patent Reference 1)    Appl. Phys. Lett. 51, 913 (1987)    (Non-Patent Reference 2)    Nature, 347, 539 (1990)